I'm on 2degrees (Welcome Bay) on a Pro1X running LineageOS, and I've had missing SMS for the last 2 or 3 weeks.
Discussions with Mrs MonCon revealed that some texts had disappeared into the ether, apparently delivered from my end, never received to her end.
Like you, I put my sim into a backup phone and it worked, then back into my PrawnX and it worked.
It's just started playing up again. On Friday I sent Mrs MC a few texts from the dining room to the lounge, and when we compared notes, again a few missing.
Don't think I've been missing any incoming, but I'll ask around, and n